I'd really like to join the Companions, but my quest - given to me by Vilkas, specifically save Heimskr from Halted Stream Camp - is, as far as I can tell, unbeatable, essential to complete in order to complete the quest line, and irreplacable. I've heard many people say they have the same issue, that they can't find the person they're supposed to save, but I haven't found ANYONE offering solutions (for console, at least). I cleared out Halted Stream Camp, and my objective is now 'Talk to Heimskr," but the quest marker tells me to go out in the middle of nowhere, west of Whiterun (as at least one other person I know of has also seen), despite Heimskr not being there; maybe he's in the sky, maybe he's underground, but he isn't where the objective marker tells me to go. Is there any patch on the way, or any way to re-assign a quest or something?

I had the same problem. If I remember right the quest marker pointed towards somewhere around whiterun stables but I couldn't find him. I eventually found him when I broke into his house long after I figured the quest was permanently broken